This invention relates generally to a butterfly valve for application within a fluid flow passageway, and more particularly, pertains to a resilient seal for use with butterfly valves which is constructed, arranged and configured relative to the butterfly valve to provide positive line contact sealing with adjoining pipe flanges in a fluid flow passageway so as to totally eliminate contamination problems which have heretofore been caused by trapped product between the seal and the adjoining flanges in prior art designs.
Butterfly or disc valves are frequently used in fluid flow lines where it is desired to load or unload fluid materials for shipment or storage. Such uses include tank trailers for transporting fluids (liquids or granular material) from one location to another, as well as fluid flow lines for loading and unloading barges, ships or other means of transportation and storage. Other uses include various pneumatic or pressure unloadings or conveyances of material which are associated with aeration devices, blowers, dusk collectors and other such devices in flow lines where some control is required.
Since butterfly valves have been used for many years in such aforementioned applications, the prior art is replete with many butterfly valve constructions and designs. The typical butterfly valve customarily uses a pivotally mounted disc-type valve in a flow line which also incorporates a resilient seal against which the disc valve moves to seal off the flow line and when open, to allow fluid materials to be conveyed along the flow line. Examples of such prior art designs includes U.S. Pat. No. 2,740,423 which discloses the typical butterfly valve construction; U.S. Pat. No. 2,994,342 which specifically discloses one type of resilient seal construction; U.S. Pat. No. 3,100,500 which provides a removable seat including seat and stemware-sleeve for the disc valve; U.S. Pat. No. 3,241,806 which discloses a plastic layer overlying a resilient seal and my prior U.S. Pat. No. 4,699,357 which provides opposed bushing mountings for a disc valve stem in a butterfly valve to provide positive disc control during repeated and continuous use.
In each of the aforementioned and other butterfly valve designs of the prior art, there has been a contamination problem when transporting such products as polymer pellets or food grade materials. Specifically, it has been discovered that plastic pellets or food products become trapped between the resilient seal and adjoining pipe flanges. For example, colored plastic pellets from a previous load might have been retained in the aforementioned contamination area and may be dislodged when discharging a load of, for example, white plastic pellets. This problem is caused in that standard butterfly valves have a radius on the edge of the resilient seal or seat. When the resilient seal or seat is compressed against a flange, the radius creates a "V" shaped crevice. The standared "O" ring sealing action of a standard seat further compounds the problem by holding the flange away from the flat edge of the resilient seal or seat. The radius edge on some hopper flange tees magnify the problem, thus providing a crevice in which product is entrapped. Unloading pressure used to unload fluid materials sometimes forces the pellets and powders into this product entrapment crevice, and in some cases, may even embed pellets into the standard resilient seal or seat in this area. It will be apparent that customer dissatisfaction, not to mention that potential for legal exposure due to contaminated product, has created a need for a new and improved design which totally and completely avoids contamination problems.